The man suspected of supplying the San Bernardino, California shooters with assault rifles was arrested by federal officers on Thursday and charged with conspiring to commit crimes of terrorism dating back to 2011.

Proposed plans included attacking a community college and a busy freeway during rush hour.

Enrique Marquez Jr., a 24-year-old resident of Riverside, California, was arrested by the FBI and charged in a three-court criminal complaint. Marquez was described by the Justice Department as a neighbor and longtime friend of Syed Farook, the gunman who carried out the December 2 attacks with his wife, Tashfeen Malik. The violent spree left 14 people dead and 21 people injured.

Marquez was charged with conspiring to provide material support to terrorists and with the unlawful purchase of two assault rifles that were used by Farook and Malik during their attack. Additionally, he was charged with defrauding immigration authorities by entering into a sham marriage with a member of Farook’s family.

According to the Justice Department, Marquez is not accused of knowing about or participating in the December 2 attack. However, he is accused of conspiring with Farook to commit terrorist acts in 2011 and 2012. Those attacks were not committed, the Justice Department said.

Meanwhile, officials believe that Marquez bought the assault rifles eventually used by Farook and Malik, as well as explosive material that was used to build a pipe bomb. They also argued that Marquez did not warn officials about Farook’s intention to commit violence.

“Mr. Marquez conspired with Mr. Farook to commit vicious attacks, as set forth in today’s charges,” said United States Attorney Eileen M. Decker. “Even though these plans were not carried out, Mr. Marquez’s criminal conduct deeply affected San Bernardino County, Southern California and the entire United States when the guns purchased by Marquez were used to kill 14 innocent people and wound many others.”

Marquez initially moved to Riverside in 2005 and met Farook, who was his neighbor. The two struck up a friendship and Farook introduced him to Islam, officials said in an affidavit. After Marquez converted, Farook introduced him to radical ideology, including the Inspire magazine published by Al-Qaeda in the Arabian Peninsula.

In 2011, the two discussed the potential to carry out violent attacks using guns and explosives, the affidavit states. In an interview with investigators, Marquez allegedly discussed these plans, which included tossing a pipe bomb into the Riverside Community College cafeteria and shooting at people from above.

Another alleged plot involved tossing pipe bombs onto the California State Route 91 freeway in order to stop traffic and shoot at those in stopped cars. Once law enforcement and first responders would arrive at the scene, Marquez and Farook planned to start shooting at them.

The final charge against Marquez alleges that he married a Russian member of Farook’s extended family so that she could gain legal status in the US. His neighbors told Reuters that they had never seen him with a woman. She allegedly paid Marquez $200 a month for his help.

Soon after the San Bernardino massacre took place, Marquez checked into a mental health facility. Reuters reported that he has been cooperating with investigators, citing unnamed sources.

According to those who knew Marquez, he was shy and not the sort of person they could imagine pulling off a violent massacre. He worked at a local bar called Morgan’s Tavern for years checking identification, and the owner said he never had a problem with Marquez.